This invention relates to a simple and effective process for preparing tocopherol concentrates.
Vegetable oil deodorizer sludge contains about 5 to 20% of tocopherols, and therefore is an important raw material for producing vitamin E and the natural antioxidants. However, the deodorizer sludge often contains substantial amount of free fatty acids, glycerides, phytosterols and hydrocarbons. The contents of free fatty acids are considerably high, ranging from about 30 to 60%. Thus, when we prepare the tocopherol concentrates from the vegetable oil deodorizer sludge, it is essential to remove these substances first, especially the free fatty acids.
Many methods for preparing tocopherol concentrates have been reported. Most of these methods involve esterification (especially methyl esterification) and high-temperature molecular distillation. The steps for such methods are very complex and require using the expensive distillation equipment and operating at a high temperature which might be a disadvantage to the heat-labile tocopherols. These methods can be mentioned as, for example, Mao and Tsen""s method (Investigation on the
Conditions for the Preparing of High-Purity Vitamin E Concentrate from Soybean Oil Deodorizer Distillate. Journal of the Chinese Agricultural Chemical Society. 33(6): 686-697, 1995, Taipei), and the methods disclosed in U.S. Pat. No. 4,454,329. (Y. Takagi and Y. Kai, Process for preparation of tocopherol concentrates. Jun. 12, 1984); U.S. Pat. No. 5,190,618 (A. G. Md. Top, et. al., Production of high concentration tocopherols and tocopherols from palm-oil by-products. Mar. 2, 1993); U.S. Pat. No. 5,616,735 (T. K. Hunt, Recovery of tocopherols. Apr. 1, 1997); U.S. Pat. No. 5,627,289 (L. J. Hilden, et. al., Recovery of tocopherol and sterol from tocopherol and sterol containing mixtures of fats and fat derivatives. May 6, 1997), and U.S. Pat. No. 5,703,252 (T. K. Hunt and J. Schwarzer, Recovery of tocopherols. Dec. 30, 1997), etc. All these methods are principally using esterification in combination with molecular distillation. These processes are all complicated, time-consuming and require high temperature treatment and expensive equipment.
On the other hand, U.S. Pat. No. 4,594,437 (Sampathkumar, Jun. 10, 1986) disclosed a process for recovering tocopherols from deodorizer sludge by using large amounts of solvent and urea to remove free fatty acids. According to the claim 1 of this patent, the amount of urea used is 5 to 25 equivalents of the fatty acids, and the amount of the solvent is 1 to 75 equivalents of urea. In additions, this method also includes heating at about 70xc2x0 C. and cooling to 0xc2x0 C., and this is very energy consuming. Furthermore, in order to recover the tocopherols, it needs to use other solvents to extract the tocopherols, for example, CHCl3 in Example 1; hexane in Example 2; CH2Cl2 in Example 3.
In additions, Lee, et al. reported a method for the concentration of tocopherols from soybean oil sludge by supercritical carbon dioxide [J Am. Oil Chem. Soc. 68(8): pp. 571-573, 1991]. However, this method also requires esterification of free fatty acids and an expensive special equipment for the supercritical carbon dioxide extraction.
The present invention provides a simple and effective process for preparing tocopherol concentrates. The method is characterized by precipitating the free acids in a mixture containing tocopherols and free fatty acids as the alkali metal salts thereof in a specific solvent that cannot, practically, dissolve the alkali metal salts of fatty acids, and recovering the tocopherols from the supernatant by removing the solvent. The specific organic solvents include acetone, ethyl acetate, dimethylformamide, acetonitrile and their mixtures.
Table 1 The main compositions of the soybean deodorizer sludge and some tocopherol concentrates.
Table 2 The result of gas chromatographic analysis revealed that the tocopherol content with solvent as DMF, acetonitrile or ethyl acetate
Table 3 The result of gas chromatographic analysis revealed that the tocopherol content with NaOH